The present invention relates to a dust collecting apparatus having a plurality of filter elements for filtering an airstream and wherein a jet of pressurized air is periodically injected in the reverse direction into the open end of each filter element to expel the accumulated particles from the outside surface of the element.
Conventional self-cleaning dust collectors of the described type typically comprise a sheet metal housing which is divided by a transverse panel having a plurality of rows of openings therein, and so that the panel defines a lower air inlet chamber and an upper air outlet chamber. Cylindrical filter elements, such as fabric filter bags or cartridge filters, are mounted so as to be in registry with the openings and they depend downwardly into the inlet chamber. In operation, the dust laden air enters the inlet chamber and the entrained particles are deposited on the outside surfaces of the filter bags, and the filtered air flows upwardly through the inside of the bags and is discharged through the upper outlet chamber.
The filter bags are periodically cleaned by means of a pulse jet, wherein a momentary (e.g. 0.1 second) jet of high velocity compressed air is directed downwardly into each bag. More particularly, the rows of bags are pulsed in sequence, and a continuous flow of air is maintained in the filtering direction since only a small number of the bags are pulsed at any given time. Also, it is conventional to mount a Venturi nozzle in the open end of each bag so that the pulsed jet of air induces additional or secondary air into the bag with the jet of air. The resulting volume of air produces a pressure pulse which travels down the length of the bag and serves to dislodge and expel the accumulated particles on the outside surface. The dislodged particles then fall downwardly into a hopper at the bottom of the housing, where they may be removed. A dust collector of this general type is disclosed in U.S. Pat. No. 3,726,066 to Colley et al and U.S. Pat. No. 5,062,867 to Klimczak.
It is recognized that the reverse pulse of air should enter the opening in the top of each filter element in a predetermined cross-sectional configuration, so as to ensure that the pulses properly impact the interior of the filter element and remove the collected contaminants from the entire flow area of the filter medium. To achieve the proper cross-sectional configuration, it is conventional to mount an insert of predetermined outline in the top of the filter element, so as to shape the entering air pulse to the desired configuration. While such inserts are satisfactory in operation, they significantly increase the cost of the apparatus.
It has also been proposed to provide a reverse pulse system which includes an annular ring above each filter, with the annular ring having very small apertures around its circumference for discharging the air into the filter in the form of a tube. The use of an annular ring of this type is also quite expensive, and it does not provide flexibility in being able to shape the cross-sectional configuration of the reverse pulse to conform to the size and shape of the filter and achieve complete cleaning thereof.
It is accordingly an object of the present invention to provide a dust collecting apparatus of the described type and which overcomes the above noted limitations and disadvantages of the prior art.
It is a more particular object of the present invention to provide a dust collecting apparatus which is adapted to provide a reverse pulse of air for each filter element, with the pulse of air having a predetermined cross-sectional configuration designed to properly impact the full area of the filtering medium so as to remove all of the collected contaminants from the exterior of the filter element, and which does not employ the use of separate inserts for this purpose.